From: Wes Turner Date: Thu, 11 Dec 2014 11:24:53 +0000 (-0600) Subject: DOC: Update templates.rst: syntax, commas X-Git-Tag: 2.8~46^2~3 X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=d40e9ba0fc205c3faa4b171eb58d239d102838de;p=thirdparty%2Fjinja.git DOC: Update templates.rst: syntax, commas --- diff --git a/docs/templates.rst b/docs/templates.rst index 81af9e29..5eec857b 100644 --- a/docs/templates.rst +++ b/docs/templates.rst @@ -5,24 +5,27 @@ Template Designer Documentation This document describes the syntax and semantics of the template engine and will be most useful as reference to those creating Jinja templates. As the -template engine is very flexible the configuration from the application might -be slightly different from here in terms of delimiters and behavior of -undefined values. +template engine is very flexible, the configuration from the application can +be slightly different from the default syntax presented here +in terms of delimiters and behavior of undefined values. Synopsis -------- -A template is simply a text file. It can generate any text-based format -(HTML, XML, CSV, LaTeX, etc.). It doesn't have a specific extension, -``.html`` or ``.xml`` are just fine. +A Jinja template is simply a text file. Jinja can generate any text-based +format (HTML, XML, CSV, LaTeX, etc.). A Jinja template +doesn't need to have a specific extension: +``.html``, ``.xml``, ``.html.jinja2``, and ``.j2`` are all just fine. -A template contains **variables** or **expressions**, which get replaced with -values when the template is evaluated, and tags, which control the logic of -the template. The template syntax is heavily inspired by Django and Python. +A template contains **variables** and/or **expressions**, +which get replaced with values when a template is *rendered*; and **tags**, +which control the logic of the template. +The template syntax is heavily inspired by Django and Python. -Below is a minimal template that illustrates a few basics. We will cover -the details later in that document:: +Below is a minimal template that illustrates a few basics using +the default Jinja configuration. We will cover +the details later in this document:: @@ -38,63 +41,85 @@ the details later in that document::

My Webpage

{{ a_variable }} + + {# a comment #} -This covers the default settings. The application developer might have -changed the syntax from ``{% foo %}`` to ``<% foo %>`` or something similar. +This example shows the default configuration settings. +An application developer can change the syntax configuration +from ``{% foo %}`` to ``<% foo %>``, or something similar. + +There are a few kinds of delimiters. The default Jinja delimiters are +configured as follows: + +* ``{% ... %}`` -- :ref:`Statements ` + like + :ref:`for-loop`, + :ref:`if`, + :ref:`macros`, + :ref:`assignments`, + :ref:`extends`, + and + :ref:`blocks` +* ``{{ ... }}`` -- :ref:`Expressions` to print to the template output +* ``{# ... #}`` -- :ref:`Comments` not included in the template output +* ``# ... ##`` -- :ref:`Line Statements ` -There are two kinds of delimiters. ``{% ... %}`` and ``{{ ... }}``. The first -one is used to execute statements such as for-loops or assign values, the -latter prints the result of the expression to the template. .. _variables: Variables --------- +Template variables are defined by the context dictionary passed to the +template. + You can mess around with the variables in templates provided they are passed in by the application. Variables may have attributes or elements on them you can access too. What attributes a variable has depends heavily on the application providing that variable. -You can use a dot (``.``) to access attributes of a variable, but alternatively -the so-called "subscript" syntax (``[]``) can be used. The following lines do -the same thing:: +You can use a dot (``.``) to access attributes of a variable in addition +to the standard Python ``__getitem__`` "subscript" syntax (``[]``). + +The following lines do the same thing:: {{ foo.bar }} {{ foo['bar'] }} -It's important to know that the curly braces are *not* part of the variable, -but the print statement. If you access variables inside tags don't put the -braces around them. +It's important to know that the outer double-curly braces are *not* +part of the variable, but the print statement. +If you access variables inside tags don't put the braces around them. -If a variable or attribute does not exist you will get back an undefined +If a variable or attribute does not exist, you will get back an undefined value. What you can do with that kind of value depends on the application -configuration: the default behavior is that it evaluates to an empty string -if printed and that you can iterate over it, but every other operation fails. +configuration: the default behavior is to evaluate to an empty string +if printed or iterated over, and to fail for every other operation. .. _notes-on-subscriptions: .. admonition:: Implementation - For convenience sake ``foo.bar`` in Jinja2 does the following things on - the Python layer: + For the sake of convenience, ``foo.bar`` in Jinja2 does the following + Python things: - - check if there is an attribute called `bar` on `foo`. - - if there is not, check if there is an item ``'bar'`` in `foo`. + - check for an attribute called `bar` on `foo` + (``getattr(foo, 'bar')``) + - if there is not, check for an item ``'bar'`` in `foo` + (``foo.__getitem__('bar')``) - if there is not, return an undefined object. - ``foo['bar']`` on the other hand works mostly the same with the a small - difference in the order: + ``foo['bar']`` works mostly the same with a small difference in sequence: - - check if there is an item ``'bar'`` in `foo`. - - if there is not, check if there is an attribute called `bar` on `foo`. + - check for an item ``'bar'`` in `foo` + (``foo.__getitem__('bar')``) + - if there is not, check for an attribute called `bar` on `foo`. + (``getattr(foo, 'bar')``) - if there is not, return an undefined object. - This is important if an object has an item or attribute with the same - name. Additionally there is the :func:`attr` filter that just looks up - attributes. + This is important if an object has an item and attribute with the same + name. Additionally, the :func:`attr` filter only looks up attributes. .. _filters: @@ -106,10 +131,13 @@ variable by a pipe symbol (``|``) and may have optional arguments in parentheses. Multiple filters can be chained. The output of one filter is applied to the next. -``{{ name|striptags|title }}`` for example will remove all HTML Tags from the -`name` and title-cases it. Filters that accept arguments have parentheses -around the arguments, like a function call. This example will join a list -by commas: ``{{ list|join(', ') }}``. +For example, ``{{ name|striptags|title }}`` will remove all HTML Tags from +variable `name` and title-case the output (``title(striptags(name))``). + +Filters that accept arguments have parentheses +around the arguments, just like a function call. For example: +``{{ listx|join(', ') }}`` +will join a list with commas (``str.join(', ', listx)``). The :ref:`builtin-filters` below describes all the builtin filters. @@ -118,15 +146,16 @@ The :ref:`builtin-filters` below describes all the builtin filters. Tests ----- -Beside filters there are also so called "tests" available. Tests can be used +Beside filters, there are also so-called "tests" available. Tests can be used to test a variable against a common expression. To test a variable or -expression you add `is` plus the name of the test after the variable. For -example to find out if a variable is defined you can do ``name is defined`` -which will then return true or false depending on if `name` is defined. +expression, you add `is` plus the name of the test after the variable. For +example, to find out if a variable is defined, you can do ``name is defined``, +which will then return true or false depending on whether `name` is defined +in the current template context. -Tests can accept arguments too. If the test only takes one argument you can -leave out the parentheses to group them. For example the following two -expressions do the same:: +Tests can accept arguments, too. If the test only takes one argument, you can +leave out the parentheses. For example, the following two +expressions do the same thing:: {% if loop.index is divisibleby 3 %} {% if loop.index is divisibleby(3) %} @@ -134,6 +163,8 @@ expressions do the same:: The :ref:`builtin-tests` below describes all the builtin tests. +.. _comments: + Comments -------- @@ -142,7 +173,7 @@ by default set to ``{# ... #}``. This is useful to comment out parts of the template for debugging or to add information for other template designers or yourself:: - {# note: disabled template because we no longer use this + {# note: commented-out template because we no longer use this {% for user in users %} ... {% endfor %} @@ -152,16 +183,18 @@ yourself:: Whitespace Control ------------------ -In the default configuration, a single trailing newline is stripped if -present, and whitespace is not further modified by the template engine. Each -whitespace (spaces, tabs, newlines etc.) is returned unchanged. If the -application configures Jinja to `trim_blocks` the first newline after a +In the default configuration: + +* a single trailing newline is stripped if present +* other whitespaces (spaces, tabs, newlines etc.) are returned unchanged + +If an application configures Jinja to `trim_blocks`, the first newline after a template tag is removed automatically (like in PHP). The `lstrip_blocks` -option can also be set to strip tabs and spaces from the beginning of +option can also be set to strip tabs and spaces from the beginning of a line to the start of a block. (Nothing will be stripped if there are other characters before the start of the block.) -With both `trim_blocks` and `lstrip_blocks` enabled you can put block tags +With both `trim_blocks` and `lstrip_blocks` enabled, you can put block tags on their own lines, and the entire block line will be removed when rendered, preserving the whitespace of the contents. For example, without the `trim_blocks` and `lstrip_blocks` options, this template:: @@ -180,8 +213,8 @@ gets rendered with blank lines inside the div:: -But with both `trim_blocks` and `lstrip_blocks` enabled, the lines with the -template blocks are removed while preserving the whitespace of the contents:: +But with both `trim_blocks` and `lstrip_blocks` enabled, the template block +lines are removed and other whitespace is preserved::
yay @@ -194,28 +227,27 @@ plus sign (``+``) at the start of a block:: {%+ if something %}yay{% endif %}
-You can also strip whitespace in templates by hand. If you put an minus -sign (``-``) to the start or end of an block (for example a for tag), a -comment or variable expression you can remove the whitespaces after or before -that block:: +You can also strip whitespace in templates by hand. If you add a minus +sign (``-``) to the start or end of a block (e.g. a :ref:`for-loop` tag), a +comment, or a variable expression, the whitespaces before or after +that block will be removed:: {% for item in seq -%} {{ item }} {%- endfor %} This will yield all elements without whitespace between them. If `seq` was -a list of numbers from ``1`` to ``9`` the output would be ``123456789``. +a list of numbers from ``1`` to ``9``, the output would be ``123456789``. -If :ref:`line-statements` are enabled they strip leading whitespace +If :ref:`line-statements` are enabled, they strip leading whitespace automatically up to the beginning of the line. -Jinja2 by default also removes trailing newlines. To keep the single -trailing newline when it is present, configure Jinja to -`keep_trailing_newline`. +By default, Jinja2 also removes trailing newlines. To keep single +trailing newlines, configure Jinja to `keep_trailing_newline`. .. admonition:: Note - You must not use a whitespace between the tag and the minus sign. + You must not add whitespace between the tag and the minus sign. **valid**:: @@ -229,18 +261,18 @@ trailing newline when it is present, configure Jinja to Escaping -------- -It is sometimes desirable or even necessary to have Jinja ignore parts it -would otherwise handle as variables or blocks. For example if the default -syntax is used and you want to use ``{{`` as raw string in the template and -not start a variable you have to use a trick. +It is sometimes desirable -- even necessary -- to have Jinja ignore parts +it would otherwise handle as variables or blocks. For example, if, with +the default syntax, you want to use ``{{`` as a raw string in a template and +not start a variable, you have to use a trick. -The easiest way is to output the variable delimiter (``{{``) by using a +The easiest way to output a literal variable delimiter (``{{``) is by using a variable expression:: {{ '{{' }} -For bigger sections it makes sense to mark a block `raw`. For example to -put Jinja syntax as example into a template you can use this snippet:: +For bigger sections, it makes sense to mark a block `raw`. For example, to +include example Jinja syntax in a template, you can use this snippet:: {% raw %}
    @@ -256,9 +288,9 @@ put Jinja syntax as example into a template you can use this snippet:: Line Statements --------------- -If line statements are enabled by the application it's possible to mark a -line as a statement. For example if the line statement prefix is configured -to ``#`` the following two examples are equivalent:: +If line statements are enabled by the application, it's possible to mark a +line as a statement. For example, if the line statement prefix is configured +to ``#``, the following two examples are equivalent::
      # for item in seq @@ -273,7 +305,7 @@ to ``#`` the following two examples are equivalent::
    The line statement prefix can appear anywhere on the line as long as no text -precedes it. For better readability statements that start a block (such as +precedes it. For better readability, statements that start a block (such as `for`, `if`, `elif` etc.) may end with a colon:: # for item in seq: @@ -293,8 +325,8 @@ precedes it. For better readability statements that start a block (such as # endfor
-Since Jinja 2.2 line-based comments are available as well. For example if -the line-comment prefix is configured to be ``##`` everything from ``##`` to +Since Jinja 2.2, line-based comments are available as well. For example, if +the line-comment prefix is configured to be ``##``, everything from ``##`` to the end of the line is ignored (excluding the newline sign):: # for item in seq: @@ -341,8 +373,8 @@ document that you might use for a simple two-column page. It's the job of In this example, the ``{% block %}`` tags define four blocks that child templates -can fill in. All the `block` tag does is to tell the template engine that a -child template may override those portions of the template. +can fill in. All the `block` tag does is tell the template engine that a +child template may override those placeholders in the template. Child Template ~~~~~~~~~~~~~~ @@ -366,12 +398,12 @@ A child template might look like this:: The ``{% extends %}`` tag is the key here. It tells the template engine that this template "extends" another template. When the template system evaluates -this template, first it locates the parent. The extends tag should be the +this template, it first locates the parent. The extends tag should be the first tag in the template. Everything before it is printed out normally and may cause confusion. For details about this behavior and how to take advantage of it, see :ref:`null-master-fallback`. -The filename of the template depends on the template loader. For example the +The filename of the template depends on the template loader. For example, the :class:`FileSystemLoader` allows you to access other templates by giving the filename. You can access templates in subdirectories with a slash:: @@ -383,12 +415,12 @@ the parent template is used instead. You can't define multiple ``{% block %}`` tags with the same name in the same template. This limitation exists because a block tag works in "both" -directions. That is, a block tag doesn't just provide a hole to fill - it -also defines the content that fills the hole in the *parent*. If there -were two similarly-named ``{% block %}`` tags in a template, that template's -parent wouldn't know which one of the blocks' content to use. +directions. That is, a block tag doesn't just provide a placeholder to fill +- it also defines the content that fills the placeholder in the *parent*. +If there were two similarly-named ``{% block %}`` tags in a template, +that template's parent wouldn't know which one of the blocks' content to use. -If you want to print a block multiple times you can however use the special +If you want to print a block multiple times, you can, however, use the special `self` variable and call the block with that name:: {% block title %}{% endblock %} @@ -421,13 +453,13 @@ readability:: {% endblock inner_sidebar %} {% endblock sidebar %} -However the name after the `endblock` word must match the block name. +However, the name after the `endblock` word must match the block name. Block Nesting and Scope ~~~~~~~~~~~~~~~~~~~~~~~ -Blocks can be nested for more complex layouts. However per default blocks +Blocks can be nested for more complex layouts. However, per default blocks may not access variables from outer scopes:: {% for item in seq %} @@ -436,10 +468,10 @@ may not access variables from outer scopes:: This example would output empty ``
  • `` items because `item` is unavailable inside the block. The reason for this is that if the block is replaced by -a child template a variable would appear that was not defined in the block or +a child template, a variable would appear that was not defined in the block or passed to the context. -Starting with Jinja 2.2 you can explicitly specify that variables are +Starting with Jinja 2.2, you can explicitly specify that variables are available in a block by setting the block to "scoped" by adding the `scoped` modifier to a block declaration:: @@ -447,7 +479,7 @@ modifier to a block declaration::
  • {% block loop_item scoped %}{{ item }}{% endblock %}
    • {% endfor %} -When overriding a block the `scoped` modifier does not have to be provided. +When overriding a block, the `scoped` modifier does not have to be provided. Template Objects @@ -455,14 +487,14 @@ Template Objects .. versionchanged:: 2.4 -If a template object was passed to the template context you can +If a template object was passed in the template context, you can extend from that object as well. Assuming the calling code passes a layout template as `layout_template` to the environment, this code works:: {% extends layout_template %} -Previously the `layout_template` variable had to be a string with +Previously, the `layout_template` variable had to be a string with the layout template's filename for this to work. @@ -470,60 +502,71 @@ HTML Escaping ------------- When generating HTML from templates, there's always a risk that a variable will -include characters that affect the resulting HTML. There are two approaches: -manually escaping each variable or automatically escaping everything by default. +include characters that affect the resulting HTML. There are two approaches: -Jinja supports both, but what is used depends on the application configuration. -The default configuration is no automatic escaping for various reasons: +a. manually escaping each variable; or +b. automatically escaping everything by default. -- escaping everything except of safe values will also mean that Jinja is - escaping variables known to not include HTML such as numbers which is - a huge performance hit. +Jinja supports both. What is used depends on the application configuration. +The default configuration is no automatic escaping; for various reasons: + +- Escaping everything except for safe values will also mean that Jinja is + escaping variables known to not include HTML (e.g. numbers, booleans) + which can be a huge performance hit. - The information about the safety of a variable is very fragile. It could - happen that by coercing safe and unsafe values the return value is double - escaped HTML. + happen that by coercing safe and unsafe values, the return value is + double-escaped HTML. Working with Manual Escaping ~~~~~~~~~~~~~~~~~~~~~~~~~~~~ -If manual escaping is enabled it's **your** responsibility to escape +If manual escaping is enabled, it's **your** responsibility to escape variables if needed. What to escape? If you have a variable that *may* include any of the following chars (``>``, ``<``, ``&``, or ``"``) you -**have to** escape it unless the variable contains well-formed and trusted -HTML. Escaping works by piping the variable through the ``|e`` filter: -``{{ user.username|e }}``. +**SHOULD** escape it unless the variable contains well-formed and trusted +HTML. Escaping works by piping the variable through the ``|e`` filter:: + + {{ user.username|e }} Working with Automatic Escaping ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ -When automatic escaping is enabled everything is escaped by default except -for values explicitly marked as safe. Those can either be marked by the -application or in the template by using the `|safe` filter. The main -problem with this approach is that Python itself doesn't have the concept -of tainted values so the information if a value is safe or unsafe can get -lost. If the information is lost escaping will take place which means that -you could end up with double escaped contents. +When automatic escaping is enabled, everything is escaped by default except +for values explicitly marked as safe. Variables and expressions +can be marked as safe either in: + +a. the context dictionary by the application with `MarkupSafe.Markup`, or +b. the template, with the `|safe` filter + +The main problem with this approach is that +Python itself doesn't have the concept of tainted values; +so whether a value is safe or unsafe can get lost. -Double escaping is easy to avoid however, just rely on the tools Jinja2 -provides and don't use builtin Python constructs such as the string modulo -operator. +If a value is not marked safe, auto-escaping will take place; +which means that you could end up with double-escaped contents. +Double-escaping is easy to avoid, however: just rely on the tools Jinja2 +provides and *don't use builtin Python constructs such as +str.format or the string modulo operator (%)*. -Functions returning template data (macros, `super`, `self.BLOCKNAME`) return -safe markup always. +Jinja2 functions (macros, `super`, `self.BLOCKNAME`) +always return template data that is marked as safe. String literals in templates with automatic escaping are considered unsafe -too. The reason for this is that the safe string is an extension to Python -and not every library will work properly with it. +because native Python strings (``str``, ``unicode``, ``basestring``) +are not `MarkupSafe.Markup` strings with an ``__html__`` attribute. +.. _list-of-control-structures: List of Control Structures -------------------------- A control structure refers to all those things that control the flow of a program - conditionals (i.e. if/elif/else), for-loops, as well as things like -macros and blocks. Control structures appear inside ``{% ... %}`` blocks -in the default syntax. +macros and blocks. With the default syntax, +control structures appear inside ``{% ... %}`` blocks. + +.. _for-loop: For ~~~ @@ -548,11 +591,11 @@ iterate over containers like `dict`:: {% endfor %} -Note however that dictionaries usually are unordered so you might want to -either pass it as a sorted list to the template or use the `dictsort` -filter. +Note, however, that **Python dicts are not ordered**; so you might want to +either pass a sorted ``list`` of ``tuple`` s -- or a +``collections.OrderedDict`` -- to the template, or use the `dictsort` filter. -Inside of a for-loop block you can access some special variables: +Inside of a for-loop block, you can access some special variables: +-----------------------+---------------------------------------------------+ | Variable | Description | @@ -590,24 +633,24 @@ each time through the loop by using the special `loop.cycle` helper::
  • {{ row }}
    • {% endfor %} -Since Jinja 2.1 an extra `cycle` helper exists that allows loop-unbound -cycling. For more information have a look at the :ref:`builtin-globals`. +Since Jinja 2.1, an extra `cycle` helper exists that allows loop-unbound +cycling. For more information, have a look at the :ref:`builtin-globals`. .. _loop-filtering: -Unlike in Python it's not possible to `break` or `continue` in a loop. You -can however filter the sequence during iteration which allows you to skip +Unlike in Python, it's not possible to `break` or `continue` in a loop. You +can, however, filter the sequence during iteration, which allows you to skip items. The following example skips all the users which are hidden:: {% for user in users if not user.hidden %}
  • {{ user.username|e }}
    • {% endfor %} -The advantage is that the special `loop` variable will count correctly thus +The advantage is that the special `loop` variable will count correctly; thus not counting the users not iterated over. If no iteration took place because the sequence was empty or the filtering -removed all the items from the sequence you can render a replacement block +removed all the items from the sequence, you can render a default block by using `else`::
      @@ -618,14 +661,15 @@ by using `else`:: {% endfor %}
    -Note that in Python `else` blocks are executed whenever the corresponding -loop did not `break`. Since in Jinja loops cannot `break` anyway, +Note that, in Python, `else` blocks are executed whenever the corresponding +loop **did not** `break`. Since Jinja loops cannot `break` anyway, a slightly different behavior of the `else` keyword was chosen. It is also possible to use loops recursively. This is useful if you are -dealing with recursive data such as sitemaps. To use loops recursively you -basically have to add the `recursive` modifier to the loop definition and -call the `loop` variable with the new iterable where you want to recurse. +dealing with recursive data such as sitemaps or RDFa. +To use loops recursively, you basically have to add the `recursive` modifier +to the loop definition and call the `loop` variable with the new iterable +where you want to recurse. The following example implements a sitemap with recursive loops:: @@ -639,15 +683,17 @@ The following example implements a sitemap with recursive loops:: The `loop` variable always refers to the closest (innermost) loop. If we -have more than one levels of loops, we can rebind the variable `loop` by +have more than one level of loops, we can rebind the variable `loop` by writing `{% set outer_loop = loop %}` after the loop that we want to use recursively. Then, we can call it using `{{ outer_loop(...) }}` +.. _if: + If ~~ -The `if` statement in Jinja is comparable with the if statements of Python. -In the simplest form you can use it to test if a variable is defined, not +The `if` statement in Jinja is comparable with the Python if statement. +In the simplest form, you can use it to test if a variable is defined, not empty or not false:: {% if users %} @@ -658,8 +704,8 @@ empty or not false:: {% endif %} -For multiple branches `elif` and `else` can be used like in Python. You can -use more complex :ref:`expressions` there too:: +For multiple branches, `elif` and `else` can be used like in Python. You can +use more complex :ref:`expressions` there, too:: {% if kenny.sick %} Kenny is sick. @@ -669,18 +715,19 @@ use more complex :ref:`expressions` there too:: Kenny looks okay --- so far {% endif %} -If can also be used as :ref:`inline expression ` and for +If can also be used as an :ref:`inline expression ` and for :ref:`loop filtering `. +.. _macros: Macros ~~~~~~ Macros are comparable with functions in regular programming languages. They are useful to put often used idioms into reusable functions to not repeat -yourself. +yourself ("DRY"). -Here a small example of a macro that renders a form element:: +Here's a small example of a macro that renders a form element:: {% macro input(name, value='', type='text', size=20) -%} {{ value|e }} {%- endmacro %} -The easiest and most flexible is importing the whole module into a variable. -That way you can access the attributes:: +The easiest and most flexible way to access a template's variables +and macros is to import the whole template module into a variable. +That way, you can access the attributes:: {% import 'forms.html' as forms %}
    @@ -925,7 +981,7 @@ That way you can access the attributes::

    {{ forms.textarea('comment') }}

    -Alternatively you can import names from the template into the current +Alternatively, you can import specific names from a template into the current namespace:: {% from 'forms.html' import input as input_field, textarea %} @@ -941,7 +997,7 @@ Macros and variables starting with one or more underscores are private and cannot be imported. .. versionchanged:: 2.4 - If a template object was passed to the template context you can + If a template object was passed to the template context, you can import from that object. @@ -950,31 +1006,31 @@ cannot be imported. Import Context Behavior ----------------------- -Per default included templates are passed the current context and imported -templates not. The reason for this is that imports unlike includes are -cached as imports are often used just as a module that holds macros. +By default, included templates are passed the current context and imported +templates are not. The reason for this is that imports, unlike includes, +are cached; as imports are often used just as a module that holds macros. -This however can be changed of course explicitly. By adding `with context` -or `without context` to the import/include directive the current context +This behavior can be changed explicitly: by adding `with context` +or `without context` to the import/include directive, the current context can be passed to the template and caching is disabled automatically. -Here two examples:: +Here are two examples:: {% from 'forms.html' import input with context %} {% include 'header.html' without context %} .. admonition:: Note - In Jinja 2.0 the context that was passed to the included template + In Jinja 2.0, the context that was passed to the included template did not include variables defined in the template. As a matter of - fact this did not work:: + fact, this did not work:: {% for box in boxes %} {% include "render_box.html" %} {% endfor %} The included template ``render_box.html`` is *not* able to access - `box` in Jinja 2.0. As of Jinja 2.1 ``render_box.html`` *is* able + `box` in Jinja 2.0. As of Jinja 2.1, ``render_box.html`` *is* able to do so. @@ -983,9 +1039,9 @@ Here two examples:: Expressions ----------- -Jinja allows basic expressions everywhere. These work very similar to regular -Python and even if you're not working with Python you should feel comfortable -with it. +Jinja allows basic expressions everywhere. These work very similarly to +regular Python; even if you're not working with Python +you should feel comfortable with it. Literals ~~~~~~~~ @@ -995,20 +1051,20 @@ for Python objects such as strings and numbers. The following literals exist: "Hello World": Everything between two double or single quotes is a string. They are - useful whenever you need a string in the template (for example as - arguments to function calls, filters or just to extend or include a + useful whenever you need a string in the template (e.g. as + arguments to function calls and filters, or just to extend or include a template). 42 / 42.23: Integers and floating point numbers are created by just writing the - number down. If a dot is present the number is a float, otherwise an - integer. Keep in mind that for Python ``42`` and ``42.0`` is something - different. + number down. If a dot is present, the number is a float, otherwise an + integer. Keep in mind that, in Python, ``42`` and ``42.0`` + are different (``int`` and ``float``, respectively). ['list', 'of', 'objects']: - Everything between two brackets is a list. Lists are useful to store - sequential data in or to iterate over them. For example you can easily - create a list of links using lists and tuples with a for loop:: + Everything between two brackets is a list. Lists are useful for storing + sequential data to be iterated over. For example, you can easily + create a list of links using lists and tuples for (and with) a for loop::
      {% for href, caption in [('index.html', 'Index'), ('about.html', 'About'), @@ -1018,15 +1074,15 @@ for Python objects such as strings and numbers. The following literals exist:
    ('tuple', 'of', 'values'): - Tuples are like lists, just that you can't modify them. If the tuple - only has one item you have to end it with a comma. Tuples are usually - used to represent items of two or more elements. See the example above - for more details. + Tuples are like lists that cannot be modified ("immutable"). If a tuple + only has one item, it must be followed by a comma (``('1-tuple',)``). + Tuples are usually used to represent items of two or more elements. + See the list example above for more details. {'dict': 'of', 'key': 'and', 'value': 'pairs'}: A dict in Python is a structure that combines keys and values. Keys must be unique and always have exactly one value. Dicts are rarely used in - templates, they are useful in some rare cases such as the :func:`xmlattr` + templates; they are useful in some rare cases such as the :func:`xmlattr` filter. true / false: @@ -1034,12 +1090,13 @@ true / false: .. admonition:: Note - The special constants `true`, `false` and `none` are indeed lowercase. - Because that caused confusion in the past, when writing `True` expands - to an undefined variable that is considered false, all three of them can - be written in title case too (`True`, `False`, and `None`). However for - consistency (all Jinja identifiers are lowercase) you should use the - lowercase versions. + The special constants `true`, `false`, and `none` are indeed lowercase. + Because that caused confusion in the past, (`True` used to expand + to an undefined variable that was considered false), + all three can now also be written in title case + (`True`, `False`, and `None`). + However, for consistency, (all Jinja identifiers are lowercase) + you should use the lowercase versions. Math ~~~~ @@ -1048,10 +1105,10 @@ Jinja allows you to calculate with values. This is rarely useful in templates but exists for completeness' sake. The following operators are supported: \+ - Adds two objects together. Usually the objects are numbers but if both are - strings or lists you can concatenate them this way. This however is not - the preferred way to concatenate strings! For string concatenation have - a look at the ``~`` operator. ``{{ 1 + 1 }}`` is ``2``. + Adds two objects together. Usually the objects are numbers, but if both are + strings or lists, you can concatenate them this way. This, however, is not + the preferred way to concatenate strings! For string concatenation, have + a look-see at the ``~`` operator. ``{{ 1 + 1 }}`` is ``2``. \- Subtract the second number from the first one. ``{{ 3 - 2 }}`` is ``1``. @@ -1059,6 +1116,7 @@ but exists for completeness' sake. The following operators are supported: / Divide two numbers. The return value will be a floating point number. ``{{ 1 / 2 }}`` is ``{{ 0.5 }}``. + (Just like ``from __future__ import division``.) // Divide two numbers and return the truncated integer result. @@ -1100,14 +1158,14 @@ Comparisons Logic ~~~~~ -For `if` statements, `for` filtering or `if` expressions it can be useful to +For `if` statements, `for` filtering, and `if` expressions, it can be useful to combine multiple expressions: and - Return true if the left and the right operand is true. + Return true if the left and the right operand are true. or - Return true if the left or the right operand is true. + Return true if the left or the right operand are true. not negate a statement (see below). @@ -1117,7 +1175,7 @@ not .. admonition:: Note - The ``is`` and ``in`` operators support negation using an infix notation + The ``is`` and ``in`` operators support negation using an infix notation, too: ``foo is not bar`` and ``foo not in bar`` instead of ``not foo is bar`` and ``not foo in bar``. All other expressions require a prefix notation: ``not (foo and bar).`` @@ -1130,9 +1188,9 @@ The following operators are very useful but don't fit into any of the other two categories: in - Perform sequence / mapping containment test. Returns true if the left - operand is contained in the right. ``{{ 1 in [1, 2, 3] }}`` would for - example return true. + Perform a sequence / mapping containment test. Returns true if the left + operand is contained in the right. ``{{ 1 in [1, 2, 3] }}`` would, for + example, return true. is Performs a :ref:`test `. @@ -1142,12 +1200,14 @@ is ~ Converts all operands into strings and concatenates them. - ``{{ "Hello " ~ name ~ "!" }}`` would return (assuming `name` is - ``'John'``) ``Hello John!``. + + ``{{ "Hello " ~ name ~ "!" }}`` would return (assuming `name` is set + to ``'John'``) ``Hello John!``. () Call a callable: ``{{ post.render() }}``. Inside of the parentheses you - can use positional arguments and keyword arguments like in python: + can use positional arguments and keyword arguments like in Python: + ``{{ post.render(user, full=true) }}``. . / [] @@ -1160,7 +1220,7 @@ If Expression ~~~~~~~~~~~~~ It is also possible to use inline `if` expressions. These are useful in some -situations. For example you can use this to extend from one template if a +situations. For example, you can use this to extend from one template if a variable is defined, otherwise from the default layout template:: {% extends layout_template if layout_template is defined else 'master.html' %} @@ -1168,7 +1228,7 @@ variable is defined, otherwise from the default layout template:: The general syntax is `` if else ``. -The `else` part is optional. If not provided the else block implicitly +The `else` part is optional. If not provided, the else block implicitly evaluates into an undefined object:: {{ '[%s]' % page.title if page.title }} @@ -1199,12 +1259,14 @@ The following functions are available in the global scope by default: .. function:: range([start,] stop[, step]) Return a list containing an arithmetic progression of integers. - range(i, j) returns [i, i+1, i+2, ..., j-1]; start (!) defaults to 0. + ``range(i, j)`` returns ``[i, i+1, i+2, ..., j-1]``; + start (!) defaults to ``0``. When step is given, it specifies the increment (or decrement). - For example, range(4) returns [0, 1, 2, 3]. The end point is omitted! + For example, ``range(4)`` and ``range(0, 4, 1)`` return ``[0, 1, 2, 3]``. + The end point is omitted! These are exactly the valid indices for a list of 4 elements. - This is useful to repeat a template block multiple times for example + This is useful to repeat a template block multiple times, e.g. to fill a list. Imagine you have 7 users in the list but you want to render three empty items to enforce a height with CSS:: @@ -1219,9 +1281,9 @@ The following functions are available in the global scope by default: .. function:: lipsum(n=5, html=True, min=20, max=100) - Generates some lorem ipsum for the template. Per default five paragraphs - with HTML are generated each paragraph between 20 and 100 words. If html - is disabled regular text is returned. This is useful to generate simple + Generates some lorem ipsum for the template. By default, five paragraphs + of HTML are generated with each paragraph between 20 and 100 words. + If html is False, regular text is returned. This is useful to generate simple contents for layout testing. .. function:: dict(\**items) @@ -1232,11 +1294,11 @@ The following functions are available in the global scope by default: .. class:: cycler(\*items) The cycler allows you to cycle among values similar to how `loop.cycle` - works. Unlike `loop.cycle` however you can use this cycler outside of + works. Unlike `loop.cycle`, you can use this cycler outside of loops or over multiple loops. - This is for example very useful if you want to show a list of folders and - files, with the folders on top, but both in the same list with alternating + This can be very useful if you want to show a list of folders and + files with the folders on top but both in the same list with alternating row colors. The following example shows how `cycler` can be used:: @@ -1259,7 +1321,7 @@ The following functions are available in the global scope by default: .. method:: next() - Goes one item a head and returns the then current item. + Goes one item ahead and returns the then-current item. .. attribute:: current @@ -1269,9 +1331,9 @@ The following functions are available in the global scope by default: .. class:: joiner(sep=', ') - A tiny helper that can be use to "join" multiple sections. A joiner is + A tiny helper that can be used to "join" multiple sections. A joiner is passed a string and will return that string every time it's called, except - the first time in which situation it returns an empty string. You can + the first time (in which case it returns an empty string). You can use this to join things:: {% set pipe = joiner("|") %} @@ -1292,21 +1354,22 @@ Extensions ---------- The following sections cover the built-in Jinja2 extensions that may be -enabled by the application. The application could also provide further -extensions not covered by this documentation. In that case there should -be a separate document explaining the extensions. +enabled by an application. An application could also provide further +extensions not covered by this documentation; in which case there should +be a separate document explaining said :ref:`extensions +`. .. _i18n-in-templates: i18n ~~~~ -If the i18n extension is enabled it's possible to mark parts in the template -as translatable. To mark a section as translatable you can use `trans`:: +If the i18n extension is enabled, it's possible to mark parts in the template +as translatable. To mark a section as translatable, you can use `trans`::

    {% trans %}Hello {{ user }}!{% endtrans %}

    -To translate a template expression --- say, using template filters or just +To translate a template expression --- say, using template filters, or by just accessing an attribute of an object --- you need to bind the expression to a name for use within the translation block:: @@ -1330,30 +1393,30 @@ tag, which appears between `trans` and `endtrans`:: There are {{ count }} {{ name }} objects. {% endtrans %} -Per default the first variable in a block is used to determine the correct -singular or plural form. If that doesn't work out you can specify the name +By default, the first variable in a block is used to determine the correct +singular or plural form. If that doesn't work out, you can specify the name which should be used for pluralizing by adding it as parameter to `pluralize`:: {% trans ..., user_count=users|length %}... {% pluralize user_count %}...{% endtrans %} -It's also possible to translate strings in expressions. For that purpose +It's also possible to translate strings in expressions. For that purpose, three functions exist: -_ `gettext`: translate a single string +- `gettext`: translate a single string - `ngettext`: translate a pluralizable string - `_`: alias for `gettext` -For example you can print a translated string easily this way:: +For example, you can easily print a translated string like this:: {{ _('Hello World!') }} -To use placeholders you can use the `format` filter:: +To use placeholders, use the `format` filter:: {{ _('Hello %(user)s!')|format(user=user.username) }} -For multiple placeholders always use keyword arguments to `format` as other -languages may not use the words in the same order. +For multiple placeholders, always use keyword arguments to `format`, +as other languages may not use the words in the same order. .. versionchanged:: 2.5 @@ -1367,15 +1430,15 @@ placeholders is a lot easier: {{ ngettext('%(num)d apple', '%(num)d apples', apples|count) }} Note that the `ngettext` function's format string automatically receives -the count as `num` parameter additionally to the regular parameters. +the count as a `num` parameter in addition to the regular parameters. Expression Statement ~~~~~~~~~~~~~~~~~~~~ -If the expression-statement extension is loaded a tag called `do` is available -that works exactly like the regular variable expression (``{{ ... }}``) just -that it doesn't print anything. This can be used to modify lists:: +If the expression-statement extension is loaded, a tag called `do` is available +that works exactly like the regular variable expression (``{{ ... }}``); except +it doesn't print anything. This can be used to modify lists:: {% do navigation.append('a string') %} @@ -1383,31 +1446,34 @@ that it doesn't print anything. This can be used to modify lists:: Loop Controls ~~~~~~~~~~~~~ -If the application enables the :ref:`loopcontrols-extension` it's possible to +If the application enables the :ref:`loopcontrols-extension`, it's possible to use `break` and `continue` in loops. When `break` is reached, the loop is terminated; if `continue` is reached, the processing is stopped and continues with the next iteration. -Here a loop that skips every second item:: +Here's a loop that skips every second item:: {% for user in users %} {%- if loop.index is even %}{% continue %}{% endif %} ... {% endfor %} -Likewise a look that stops processing after the 10th iteration:: +Likewise, a loop that stops processing after the 10th iteration:: {% for user in users %} {%- if loop.index >= 10 %}{% break %}{% endif %} {%- endfor %} +Note that ``loop.index`` starts with 1, and ``loop.index0`` starts with 0 +(See: :ref:`for-loop`). + With Statement ~~~~~~~~~~~~~~ .. versionadded:: 2.3 -If the application enables the :ref:`with-extension` it is possible to +If the application enables the :ref:`with-extension`, it is possible to use the `with` keyword in templates. This makes it possible to create a new inner scope. Variables set within this scope are not visible outside of the scope. @@ -1420,8 +1486,8 @@ With in a nutshell:: {% endwith %} foo is not visible here any longer -Because it is common to set variables at the beginning of the scope -you can do that within the with statement. The following two examples +Because it is common to set variables at the beginning of the scope, +you can do that within the `with` statement. The following two examples are equivalent:: {% with foo = 42 %} @@ -1440,7 +1506,7 @@ Autoescape Extension .. versionadded:: 2.4 -If the application enables the :ref:`autoescape-extension` one can +If the application enables the :ref:`autoescape-extension`, one can activate and deactivate the autoescaping from within the templates. Example:: @@ -1453,4 +1519,4 @@ Example:: Autoescaping is inactive within this block {% endautoescape %} -After the `endautoescape` the behavior is reverted to what it was before. +After an `endautoescape` the behavior is reverted to what it was before.